The invention relates in general to heat exchangers and in particular to a new and useful method for controlling the heat of heat yielding gases to be supplied to a heat exchanger, and to an apparatus for the practice of this method.
In the cooling of gases obtained under gas side pressure and at high temperatures, as e.g. in the partial oxidation of oil, asphalt, oil shale or coal, the gases are laden with pollutants which lead to high or low temperature corrosion. By German Pat. Nos. 1,918,171 and 1,751,085 waste heat boilers have been proposed whereby it is possible to generate high pressure steam at smallest tube wall overtemperature while yet remaining below the high temperature corrosion limit.
As the gases are laden with amorphous soot or coke and ash particles, the heat transfer of the waste heat boiler becomes worse with increasing fouling. To counteract this, the exchanger surfaces of the boiler have been made oversize in order to have large reserves available and to achieve a long period of use between two cleaning periods. Another option is to use special cleaning possibilities, e.g. variation of the gas velocity during the operation itself.
With certain heat exchangers, e.g. with superheaters, in like manner corrosion occurs below a certain tube wall temperature making it necessary to control and to influence this tube wall temperature during operation, without the continuous operation of the installation being impaired. But if e.g. a saturated steam generator is followed by a superheater, it is not possible to provide heating surface reserves in the vaporization zone, because if the gas is cooled too much, the desired hot steam temperature is no longer obtainable.